1. Field of the Invention
The present invention relates to a nonaqueous electrolyte secondary battery including a flat wound electrode body.
2. Description of Related Art
A nonaqueous electrolyte secondary battery such as a lithium ion secondary battery (also referred to as “lithium ion battery”) has a lighter weight and higher energy density than existing batteries. Therefore, a nonaqueous electrolyte secondary battery has been preferably used as a high-output power supply mounted on a vehicle or as a power supply for a PC or a portable device. In particular, a light-weight lithium ion secondary battery capable of obtaining high energy density is preferably used as a high-output power supply for driving a vehicle such as an electric vehicle (EV), a hybrid vehicle (HV), or a plug-in hybrid vehicle (PHV).
In a typical configuration of this nonaqueous electrolyte secondary battery, a structure is known in which an electrode body, which includes a positive electrode and a negative electrode with a separator interposed therebetween, and a nonaqueous electrolytic solution are accommodated in a battery case. In particular, in order to stably supply a high current, a nonaqueous electrolyte secondary battery used in a power supply for driving a vehicle includes a wound electrode body which is formed by making elongated belt-shaped positive and negative electrodes overlap each other with a separator interposed therebetween to obtain a laminate and winding the laminate. For example, Japanese Patent Application Publication No. 2014-154291 (JP 2014-154291 A) discloses a technique relating to this battery.
In this nonaqueous electrolyte secondary battery, a gap between the positive and negative electrodes in the wound electrode body is filled with an appropriate amount of the nonaqueous electrolytic solution, which contributes to the movement of charges between the positive and negative electrodes. On the other hand, when the inside of the wound electrode body is filled with an excess amount of the nonaqueous electrolytic solution, a decrease in performance such as an increase in battery resistance may occur. In a nonaqueous electrolyte secondary battery of the related art, when an excess amount of a nonaqueous electrolytic solution is supplied into a battery case by mistake, an excess amount of the residue of the nonaqueous electrolytic solution is likely to accumulate in a lower portion of the wound electrode body (that is, a portion of the electrode body that is positioned on the bottom of the battery case when the electrode body is accommodated in the battery case).